Forum: F-22A Raptor

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

Raptorclaw wrote:

Unfortunately, (no USAF requirement) + (no $$$ for 'extras') = (no F-22 autothrottle). Same goes for a speed hold autopilot mode coupled to the engines. Although, I believe (not totally sure) that option may be among the autopilot options tentatively planned for future upgrades.

The airlines rarely do something for free. Either the manufacturers make them, unions make them, the FAA or the NTSB acting through the FAA does. Autothrottles are there mostly for situational awareness. As much as it sounds odd to say this, the less time a pilot spend flying the plane the better. Meaning, the less time his head is in the box, the more it's managing the situation, ie allowing him/her to see the forest through the trees. I would think that would find a key role in an attack mission. The more the a/c does on it's own, the more the pilot can manage the accuracy of the attack. Also of primary concern is crew stress and fatigue. A less stressful entry and exit from battle allow for a more alert pilot when the situation requires it most.

The airspeed function, usually called Flight Level Change of "FELCH" as slang is where you see the throttles move on their own the most. "Felch 250" (knots) and the aircraft will maintain that up to or down to the selected altitude within the limits of the a/p roll over smoothness and pitch/ airspeed limits. If a F-22 is doing mach 1.8 at 60K, then all the pilot has to do is select a lower altitude and hit FLC and the aircraft will maintain 1.8 to the new altitude (not accelerate in the dive). Nice if he has other things to worry about like monitoring enemy radar detection ranges, or (whatever) etc. I flick of the heading bug and he takes a 15 degree turn to skirt a sam site. Minimal effort, maximum situational awareness.

It's interesting to look at design cycles. It's well known how long the F-22 gestated depending on where you start counting (81/96?). The Plane I flew was announced as a concept around 1999, and I was flying it as a line pilot in 2004, a 5 year cycle. While many feature of it weren't anything new, apparently it shares the same circuits board arrangements as the F-22. I just can think of the acronym for it off the top of my head, though it's likely similar but different with a different name in the F-22.

If the make the effort to retrofit autothrottles at some point, then and engine trim system could be added at the same time with no hardware and some software if they were so inclined.

Interesting anyway, thanks for the info.

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Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

Raptor claw, perhaps you can tell me at least in concept how similar this is to what the Air Force General was referring to when he said, "the F-22 doesn't have a radio per se, rather a blank circuit board that were program ""today you are a radio""

http://www.aviationtoday.com/cgi/av/sho ... ionics.htm

I flew the EMB-170 with the Primus epix, considered the most advanced avionics package commercially available and FBW

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

"Avionics share as large a part in the success of a fighter as the ability to maneuver and fly fast, or to "turn and burn". F-22 avionics reflect the quantum leaps in computer technology in the last 10 years. "Integrated" means that the F-22 can take information from many sources, compare that information and determine a single, consistent picture of the world around the pilot. In addition to these external inputs gathered by the F-22's own sensors, several F-22's can exchange information by means of the aircraft Inter/Intra Flight Data Link (IFDL) and additional information can be gathered from off board sensors like E 3 Airborne Warning and Control System (AWACS) aircraft and satellites.

Integrated avionics have some unusual characteristics. The F-22 has no radios, navigation gear like TACAN or Global Positioning System (GPS) or Instrument landing System (ILS) or even a radar in the traditional sense.

The Common Integrated Processor modules have the ability to emulate any of the electronic functions through automatic reprogramming. For example, if the CIP module that is acting as radio dies, one of the other modules will automatically reload the radio program and take over the radio function. This approach to avionics makes the equipment extremely tolerant to combat damage as well as flexible from a design upgrade point of view.

The aircraft's avionics architecture remains flexible to accept future upgrades without having to design and retrofit new hardware to the fighter."

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

It would seem similar but the F-22 can reprogram on the go more??

bf-fly wrote:

"Avionics share as large a part in the success of a fighter as the ability to maneuver and fly fast, or to "turn and burn". F-22 avionics reflect the quantum leaps in computer technology in the last 10 years. "

Actually, an interesting fact is that they abandoned the F-22's Event Based FCS architecture and went back to the Time Based FCS model with the F-35. It seems that the F-22's architecture proved difficult to tweak right and can potentially be rather catastrophicallly wrong. The traditional Time based system is competent enough in function and are much more predictable in development.

bf-fly wrote:

Raptor claw, perhaps you can tell me at least in concept how similar this is to what the Air Force General was referring to when he said, "the F-22 doesn't have a radio per se, rather a blank circuit board that were program ""today you are a radio""

Actually I know very little about on-aircraft hardware, especially anything related to avionics. As you probably know, all the avionics (which included 'radio' functionality) was done by Boeing. All the FLCS (control laws, including autopilot) design and mechanization work was done by LM in Ft. Worth. There was really very little crosstalk between the two functions....

As to the autothrottle issue, I didn't intend to give you the impression that there are no autopilot modes in the F-22, there certainly are. For whatever reason, USAF didn't ask for a speed-hold mode, at least not in the 'baseline' version.

bf-fly wrote:

Considering the size of the F-22 massive rudders, I suspect anything above about 20 knots and they start to be effective.

The issue comes down not so much to airspeed (although you have to have some, at least), but more to AOA. Normally, very slow airspeeds are coincident with very high AOAs. Unfortunately, at these AOA's the rudders are basically completely blanked and don't have any significant control power. They begin to lose usefulness somewhere in the 20's (degrees AOA) and are completely worthless at some AOA above that. Differential tail becomes the primary yaw control device at these AOA's.

dwightlooi wrote:

Actually, an interesting fact is that they abandoned the F-22's Event Based FCS architecture and went back to the Time Based FCS model with the F-35. It seems that the F-22's architecture proved difficult to tweak right and can potentially be rather catastrophicallly wrong. The traditional Time based system is competent enough in function and are much more predictable in development.

I'm a little confused as to exactly what you mean when you say "FCS architecture" being Event Based vs Time Base. The F-22 FLCS (the control laws) runs continously, at a constant frame rate, always has. Perhaps it's just a terminology issue, and you are referring to something completely different???

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

I only have a couple of seconds to spare.

1)I'm sure the F-22 has an excellent A/P, just speed control we were talking about 2) without checking, I'm assuming the F-22 has a faster processor since airlines want lock solid reliability first 3) Dwight, that was a quote, not my words, more I intended to highlight the blank card type system that a re programmed to the needed function. For airlines it's a line maintenence function, but the Raptor can do more of it itself.

gota go

Active Member Joined: Aug 28, 2006 - 05:58 AM Posts: 191

Raptor claw-- lower section for Dwight (I think)

Quote:

The issue comes down not so much to airspeed (although you have to have some, at least), but more to AOA. Normally, very slow airspeeds are coincident with very high AOAs. Unfortunately, at these AOA's the rudders are basically completely blanked and don't have any significant control power. They begin to lose usefulness somewhere in the 20's (degrees AOA) and are completely worthless at some AOA above that. Differential tail becomes the primary yaw control device at these AOA's.

True enough, though from my perspective "when they become effective" is intended more as a dryer term. ie, rolling down the runway, when do the rudders begin to "bite" so to speak and begin to have control effectiveness. AOA blanking is a very valid point but also returns me as to why an engine trim system isn't integrated. I can tell you that absolutely that a much smaller power split "influences" where the nose points. That is not to say that as you stated a idle/AB split would not wouldn't be a much larger effect, but also more taxing on the engines and systems. A more subtle split would actually be quite surprising what it can do, and also in conjunction with the last bits of effective rudder. It will move the nose quite effectively. Example, my plane doesn't have nosewheel steering and has close coupled (tail) centerline thrust engines. Anything under about 5 mph I have to use differential brakes to turn sharply, but after that differential power alone is quite sufficient to turn the aircraft (not tight mind you). That includes the friction of the wheels resisting the turn, in flight n/a. I know this is minutia, and clearly you are correct about the $$$ issues. From from my perspective, it's really just not that hard to design and build (mostly software), but ultimately at this point perhaps deemed not required. At this point the maneuverability of the F-22 is more of an insurance policy. When the day comes (if ever) that an a/c can fairly consistently defeat A2A missiles through endgame maneuverability, then I suspect ever last ounce of maneuverability will be wrought from every airframe. Since at this stage anyway, stealth/space/$$$ requirement preclude the 3rd TVC element, I understand why it's not included yet. But for those who wish to degrade the F-22 for not having 3D, it's is the easiest to achieve should the decision be made and does not require a TVC hardware redesign/retrofit.

It may not be practical for other considerations, but in fact, it's the easiest element of control (of 3) to achieve through thrust alone. Which of course returns us to Sioux City/DC-10. The asymmetric thrust creates yaw first, but also creates "side effects". Example, all applications/reductions of power will raise or lower the nose the nose. Asymmetric power intended to create yaw also speeds up the outside wing in the newly created turn. When the wing moves faster, more lift is created, lifting the wing, ie, a small bank also results.

So they added power on the right engine to turn left (example). Remember the DC-10 has engines on the wing, so the arm (distance) of change amplifies the effect. Power is added to the right, reduced left. The right wing also raises due to increased lift from the higher speed amplifying the effect. But the nose raises (typically but not always depending on CG, C Lift and flap position) due to the power increase. SO, it turns left and the nose raises, OK, cool. Now stop the turn..., yikes..., opposite applications. Now we're looking at inertia. Even more power split is require to stop the turn. OK it works, now you yank to power back to stop the overturning the other direction...., the nose falls, then you must add symetric power to bring it back up..., etc, etc...,

Now we have oscillation's. If you look at the flight profile of the DC-10, that's what got it. Not so much the ability to turn, but the ability to control the oscillations, mostly vertical. Look at the crash- they were in an oscillation (if I recall correctly) and were unable to get the nose up in time.

Very impressive job of flying. Superb Cockpit Resource Management. A tragedy and a success at the same time.

Now if you interject computer control and FBW into that equation to tame the oscillations...,

dwightlooi wrote:

The interesting thing in those pictures at the beginning of this thread is not that the F-22 is flying with wing tanks (thats neither surprising nor interesting). The interesting thing is the way they are jetisoned. With just about EVERY other jet fighter, you jetison the tanks from the pylons. In the pictures, the F-22 jetisons the pylons from the aircraft with the tanks still attached. It makes sense from a stealth perspective and I have always suspected that the F-22 and F-35s will have inflight jetisonable pylons. But this is the first time I have seen it for real!

The wing tank fuel pylons on the F-16 are jettisoned with the tank. The centerline tank hangs from a MAU-12 so the centerline pylon stays with the aircraft. Here's the link to the tank supplier:
http://www.sargentfletcher.com/eft.htm
Fisk

fiskerwad wrote:

The wing tank fuel pylons on the F-16 are jettisoned with the tank. The centerline tank hangs from a MAU-12 so the centerline pylon stays with the aircraft.

Confirming Fisk on that... Thumb

Question, will the F-35 have a similar pylon jettison system?

PhillyGuy wrote:

Question, will the F-35 have a similar pylon jettison system?

Based on the press releases on this link, PhillyGuy:
http://www.sargentfletcher.com/eft.htm
I'm guessing yes? Wink

Fisk

Forum: F-22A Raptor

Any shots of the F-22 flying with four tanks yet?